The need for chemically and biologically pure water in the aforementioned kinds of laboratories is presently most commonly met by the use of bottled distilled water. This has a number of disadvantages. First, even freshly distilled water is not of ultra high purity unless it is repeatedly distilled in distillation equipment which assures against contamination during distillation. Secondly, even where the freshly distilled water is of ultra high purity, contamination from its container or otherwise can occur, and in the absence of stringent precautions does occur, particularly during extensive periods of storage. Added to this is the fact that the purity requirements for the water can vary, even within one laboratory, depending upon the nature of the experimental or other work being conducted, ordinary single-distilled water being satisfactory in some instances and ultra high purity water being required in others.
It is well known that water can be stripped of its ionized impurities by flowing it through a column of ion-exchange resin and that water can be stripped of absorbed impurities and of various non-ionized dissolved impurities by flowing it through a column of activated charcoal. Also, it is known that water can be stripped of bacteria by passing it through a sub-micron pore size membrane. Hence, it would be possible for a laboratory worker to purify water by passing it through these three media. However, this would, like the use of bottled distilled water, involve considerable trouble and expense and would, absent additional trouble and expense, provide no control over the extent to which the water would be purified to the end that in some instances the water would be more pure, and in other instances less pure, than required for the particular work being conducted. Still further, absent other precautions, the water so prepared could be less pure biologically than prior to such treatment particularly in that the arrangement of the media and other components of the system could, and likely would, be such as to present hazard of greater rather than lesser bacterial contamination of the treated water.
Hence, there is need for a convenient, relatively inexpensive and reliable water purification device which enables a worker to controllably treat water to the degree of purity and in the quantities as needed. The present invention fulfills this need.